Field of the Invention
The present disclosure generally relates pattern recognition and, more particularly, to a pattern recognition apparatus, a pattern recognition method, a storage medium, and to a technique used for recognizing an object from an image obtained by an imaging unit.
Description of the Related Art
As a pattern recognition method, for example, a technique discussed in Mustafa Ozuysal, Pascal Fua, Vincent Lepetit, “Fast Keypoint Recognition in Ten Lines of Code,” cvpr, pp. 1-8, 2007 IEEE Conference on Computer Vision and Pattern Recognition, 2007 has been known. This technique uses a binary code obtained by comparing pixel values of a reference point pair of an input image as an image feature amount, and achieves pattern recognition processing by referring to a previously-learned dictionary table based on the binary code.
Other examples of the background art include a technique discussed in Japanese Patent Application Laid-Open No. 2010-273112. This technique calculates a degree of association indicating a degree of matching between a feature amount of each person whose head is detected on a past frame image and a feature amount of each person whose head is detected on the current frame image. The heads between which the degree of association is higher than or equal to a threshold and is the maximum are determined to be the head of the same person.
Other examples of the background art include a technique discussed in Japanese Patent Application Laid-Open No. 2009-301088. This technique searches a learning image for learning reference pixels in a plurality of directions from a pixel of interest in the learning image. A reference pixel code calculation unit calculates a bit code serving as a learning reference pixel code from a feature amount comparison value. A reference pixel statistic amount calculation unit calculates a reference pixel statistic amount of learning reference pixels obtained from a plurality of learning images for each event where an input image differs from the learning images. An input pixel code calculation unit calculates an input pixel code from a feature amount comparison value between a pixel of interest in the input image and an input reference pixel lying in a search direction in the input image. An event determination unit determines the occurrence of an event at the pixel of interest in the input image based on the input pixel code and the reference pixel statistic amount. A change of illumination is described as the event.
Other examples of the background art include a technique discussed in Japanese Patent Application Laid-Open No. 2006-185206. This technique generates a background probability value table based on time-series images of a background, and generates a background threshold table indicating a threshold of a degree of similarly to the background based on the time-series images of the background.
Any one of bit codes is assigned to each pixel of interest included in an area of interest of an input image by determining a brightness difference from other pixels. A probability value at which the code of each pixel of interest occurs is determined by referring to the background probability value table for each code. Based on the probability value, the degree of similarity of a pixel area of interest to the background is calculated. The degree of similarity is compared with the threshold of the corresponding pixel area in the background threshold table, whereby whether the pixel area of interest corresponds to an object is determined.
However, according to the technique discussed in Mustafa Ozuysal, Pascal Fua, Vincent Lepetit, “Fast Keypoint Recognition in Ten Lines of Code,” cvpr, pp. 1-8, 2007 IEEE Conference on Computer Vision and Pattern Recognition, 2007, processing accuracy may degrade if the calculation results of feature amounts in the pixel positions include an error due to noise or blocking.
The technique discussed in Japanese Patent Application Laid-Open No. 2010-273112 is premised on that the feature amounts in the pixel positions are appropriately calculated in the first place. An adverse effect can thus occur on post-processing if the calculation results of the feature amounts in the pixel positions include an error due to noise or blocking.
Similarly, the technique discussed in Japanese Patent Application Laid-Open No. 2009-301088 is also premised on that the feature amounts in the pixel positions are appropriately calculated. The technique therefore does not accommodate situations where the calculation results of the feature amounts in the pixel positions include an error due to noise or blocking.
Similarly, the technique discussed in Japanese Patent Application Laid-Open No. 2006-185206 does not accommodate situations where luminance values in the pixel positions include an error (a value irrelevant to an object to be recognized) due to noise or blocking.